Electrode feed using plural motors having constant speed drooping characteristics

ABSTRACT

A semi-automatic or automatic welding apparatus using two or more motors having drooping characteristics approximating constant speed for feeding a consumable welding electrode wire, wherein the distance from a wire reel to a welding torch is increased, and the portable portion reduced in size and weight, whereby the maneuverability and portability of the semi-automatic or automatic welding apparatus are improved and the stability of the wire feed is enhanced.

United States Patent [151 3,679,864

Tanegashima et al. 1 July 25, 1972 [541 ELECTRODE FEED USING PLURAL3,279,669 10/1966 Bernard et al. ..226/181 MOTORS HAVING CONSTANT SPEED3 522 332 532? gg X g en et ..219/130 x DROOPING CHARACTERISTICS3,396,888 8/1968 Rygiol ..226/181 x [72] Inventors: KenlchiroTanegmhlma, lkeda-shi;Makoto 3,443,145 5/19 9 g aim. ...2l9/l30X K b hj,Ni hi i hi; shi i hi 3,506,174 4/1970 Shuey, Jr... ..226/108 Kudo,Kawanishi-shi, all of Japan 2,636,102 4/1953 LObOSCO ..219/13 1 I3,249,839 5/1966 Fay ..318/345 1 Asslsneer Mmushm lnd'mflfl 3,414,79112/1068 Munson et al. ..318/345 Osaka, Japan o [22] Filed: 1969 PrimaryExaminer-R. F. Staubly [211 A N 887,044 Assistant Examiner-George A.Montanye Atmmey-Stevens, Davis, Miller & Mosher 30 Foreign ApplicationPriority Data Dec. 26, 1968 Japan ..44/689 [57] ABSIRACT Asemi-automatic or automatic welding apparatus using two [52] US. Cl...219/130, 219/69, 219/72, or more motors having droopingcharacteristics approximat- 226/ 108, 226/181 ing constant speed forfeeding a consumable welding elec- [51] Int. Cl. ..B23k 9/00 trode wire,wherein the distance from a wire reel to a welding [58] Field of Search..219/ 130, 74; 228/ 184, 181, torch is increased, and the portableportion reduced in size 228/108; 314/68, 69, 72 and weight, whereby themaneuverability and portability of the semi-automatic or automaticwelding apparatus are im- [56] References Cited proved and the stabilityof the wire feed is enhanced.

UNITED STATES PATENTS I g 2Claims,4DrawinglYgures 2,790,925 4/1957Landisetal. "314 9 ELECTRODE FEED USING PLURAL MOTORS HAVING CONSTANTSPEED DROOPING CHARACTERISTICS The present invention relates to asemi-automatic or an automatic apparatus using two or more motors forfeeding a consumable welding electrode wire (hereinafter referred to asa wire for simplicity), wherein the distance from a wire reel to awelding torch is increased and the portable portion reduced in size andweight, so as to improve the maneuverability and portability ofsemi-automatic or automatic welding apparatus and to enhance thestability of the wire feed.

FIG. I is a view schematically showing the construction of aconventional welding apparatus;

FIG. 2 is a diagram showing the relationship between the wire feedingforce and the wire feeding rate in the conventional welding apparatus;

FIG. 3 is a circuit diagram of an embodiment of the welding apparatusaccording to the present invention; and

FIG. 4 is a diagram showing the relationship between the wire feedingforce and the wire feeding rate in the welding apparatus of the presentinvention.

It is already known to employ two or more motors for feeding a wire, forthe purpose of increasing the distance from a wire reel to a weldingtorch. Namely, as shown in FIG. I, a wire 2 drawn from a wire coil 1 isintroduced into a first guide tube 6 by the co-action of a first feedroller 4, driven from a first feed motor 3, and a press roller 5, andthen into a second guide tube 10 with a force imparted thereto by asecond feed roller 8, driven from a second feed motor 7, and aco-operating second press roller 9 which are provided between the exitend of the first guide tube 6 and the entrance end of the second guidetube 10, and which are finally fed to an arc portion 12 through acontact tip 1] of the torch. A welding current flows from one of theoutput terminals of a power source 13 to the other output terminal ofthe same through the contact tip ll of the torch, the wire 2, the arcortion 12 and a material 14 to be welded.

In a conventional welding apparatus of the type described above, twomotors of the characteristics shown in FIG. 2 have been used incombination, so as to obtain a smooth wire feed.

FIG. 2 is a diagram showing the relationship between the wire feedingforce and the wire feeding rate of each motor (including the feedroller), wherein M M represent the characteristic of the first feedmotor and M represents the characteristic ofthe second feed motor.

The second feed motor is occasionally of the characteristic representedby M With reference to FIG. 2, if the operational characteristic of thefirst feed motor is set as represented by the line M and thecharacteristic of the second feed motor as represented by the line M theforce F required for feeding the wire will be the sum of the force F,imparted by the first feed motor and the force F imparted by the secondfeed motor, i.e. F F and the wire feeding rate will be v,.

The force F required for feeding the wire is variable depending upon thelengths and bending degrees of the first guide tube and the second guidetube, and the wire diameter. Therefore, if the bending degree of eachguide tube varies in the welding operation, the force F will be changedaccordingly.

When the force F required for feeding the wire is increased by AF, theoperational position of this prior art apparatus is shifted from thepoint P to the point P', on the characteristic line M in FIG. 2, so thatthe wire feeding rate is decreased by AV and the feeding force of thefirst feed motor is increased by AF.

When the second feed motor is of the characteristic M the feeding forcethereof remains at F whereas when it is of the characteristic M theoperating point moves from the point P to the point P g and the wirefeeding force is slightly increased from F However, since the droopingdegree of M is generally selected to be large, the increase is small andthe wire feeding force can be regarded essentially as P Further, it isusual that the drooping degree of the operational characteristic line Mof the first feed motor is small or, in other words, the value of AV/AFis small so that the value of AV will not give a substantial effect onthe welding operation in relation to the value ofAF which occurs undernormal welding operation. In order to change the wire feeding rate, theoperational characteristic line of the first feed motor is reset at Mfrom M whereby the wire feeding rate is elevated to V and the feedingforce imparted to the wire becomes the sum of F created by the firstfeed motor and F or F created by the second feed motor.

As stated above, in the conventional welding apparatus of the type usingtwo or more wire feed motors, a motor (including its control element)having a wire feeding rate vs. wire feeding force characteristic of asmall drooping degree (a characteristic approximating the constant speedcharac-' teristic) has been combined with a motor characterized by alarge drooping degree (a characteristic approximating the constantfeeding force characteristic), and the wire feeding rate has been set bythe feed motor having a small drooping degree, while the feed motorhaving a large drooping degree has been used by previously setting it ata predetermined operational characteristic line M or M Furthermore, thewire feeding force of the motor of a small drooping degree is usuallyabout 4l0 times greater than that of the motor of a large droopingdegree.

As such, in the case of selecting a characteristic approximating theconstant feeding force characteristic for one of the feed motors, if thenecessary wire feeding force is varied, such variation will be almostentirely borne by the feed motor having a characteristic approximatingthe constant speed characteristic.

Generally, the feed motor having a characteristic of a large droopingdegree approximating the constant feeding force characteristic islocated interior of or adjacent to the torch, and the feed motor havinga characteristic of a small drooping degree approximating the constantspeed characteristic is located adjacent to the wire reel. Therefore, anincrease in the necessary wire feeding force is imparted to the wire asan in creased wire inserting force.

A wire of small diameter is strong against tension but weak against anaxial pushing force and is susceptible to buckling. Therefore, theapplication of an excessively large inserting force has resulted inbuckling of the wire, which is not only detrimental to the passage ofthe wire through the guide tubes but also presents the possibility thatthe feed motor controlling elements overloaded.

The present invention has been made with a view to eliminating suchdrawbacks of the conventional apparatus. A practical embodiment of thewelding apparatus according to the present inventionis shown in FIG. 3and the relationship between the wire feeding force and the wire feedingrate of the apparatus is shown in FIG. 4.

Referring first to FIG. 3, numeral lSdesignates a control powertransformer having a primary coil l6; 17 a secondary coil of saidtransformer 15 having a neutral point l8; I9, 20 rectifier diodes; 21 afirst feed motor; 22 a second feed motor; 23 a silicon controlledrectifier; 24 a reverse voltage preventing diode inserted in a gatecircuit of said silicon controlled rectifier 23; and 25 a pulsegenerating transformer.

Where a third feed motor is necessary, such may be connected in parallelwith the first feed motor 21 and the second feed motor 22. Numerals 26,27, 28 and 29 designate a transformer, a diode, a capacitor and aresistor respectively of a reference voltage circuit; and numeral 30designates a reference voltage adjusting resistor by which a wirefeeding rate is set. Across resistor 30 is developed a voltage in adirection opposite to the direction of the induction voltages of themotors 21, 22, and a difference between said voltage and the higher oneof the induction voltages of the motors 21, 22 is impressed across thebase 32 and the emitter 33 of a transistor 31 through an overvoltageprotecting circuit, consisting of a resistor 34 and a Zener diode 35,and a smoothing and stabilizing circuit consisting of resistors 36, 37and capacitors 38. 39. Numerals 40, 41, 41 and 43 designate atransformer, a diode, a resistor and a Zener diode respectively of apulse generating source circuit and a rectangular wave is generatedacross the opposite ends of the Zener diode 43. The emitter 33 and thecollector 44 of the transistor 31, a resistor 45 and a pulse generatingcapacitor 46 are connected in series with each other and connected inparallel with the Zener diode 43.

A resistor 47, a uni-junction transistor. (hereinafter abbreviated asUJT) 48 and-the primary coil 49 of a pulse generating transformer areconnected in series and the series circuit thus formed connected withthe opposite ends of the Zener diode 43. The emitter 50 of the UJT 48 isconnected to one terminal of the capacitor 46 as shown.

The relationship between the wire feeding force and the wire feedingrate, obtained by the circuit of FIG. 3, is as shown in FIG. 4, and thewire feeding rate is controlled in the follow ing manner: Suppose thatthe voltage of the resistor 30 is set at E, and the higher one of theinduction voltages of the wire feed motors 21, 22 is E When E,E,, issmoothed and impressed across the base 32 and the emitter 33 of thetransistor 31, the impedance Z of the transistor 31 is varied accordingto the value of said differential voltage and the charging rate of thecapacitor 46 is also varied. When the terminal voltage of the capacitor46 has reached the peak voltage of the UJT 48, the charge stored in thecapacitor 46 is instantaneously discharged through the primary coil 49of the transformer 25. In this case, a pulse is generated in thesecondary coil and the gate of the silicon controlled rectifier 23 istriggered by said pulse. Thus, the silicon controlled rectifier 23 isignited. When E,-E,, is large, the striking phase of the arc isadvanced, with the rates of rotation of the motors 21, 22 increasing,whereas when the same is small, the striking phase of the arc is delayedwith the rates of rotation of said motors decreasing.

Although the rotational speeds of the first feed motor 21 and the secondfeed motor 22 are controlled in the manner described, they tend to loweras the mechanical load, imposed on the respective motors, increases.This is not only because each motor itself has such a characteristicthat the number of revolutions thereof tends to decrease as the loadincreases, but also because the control circuit of FIG. 3 also has suchan operational characteristic that E,E must be made large for giving alarge input to the motor. I I

Referring now to FIG. 4, the voltages impressed on the first feed motor21 and the second feed motor 22 are always the same because these motorsare connected in parallel with each other. Let it be supposed that theoperational characteristic line of the first feed motor 2] is set at M,,and that of thesecond feed motor 22 at M If a total force of F isrequired for feeding the wire under such conditions, F is divided intoF,, a share taken by the first feed motor 21, and F a share taken by thesecond feed motor 22, and the share ratio is determined by the relationbetween M,, and M,,.

Namely, if the operational characteristic lines M,, and M,, areapproximately represented by the equations V A, B,F, (expression ofrelation between the wire feeding rate V and the wire feeding force F,on one operational characteristic line) Va A2 B2B (expression ofrelation between the wire feeding rate K and the wire feeding force F2on another operational ch'zfiic'teristic line),

wherein A,, A B, and B each are constants, F,, F and V, are determinedunder conditions of A, -B,F,=A B. ,F. V, wherein V, is the feeding rateof the wire when the wire is fed by the first feed motor 21 and thesecond feed motor 22 being in an equilibrium state.

When the force F necessary for feeding the wire is increased by AF inFIG. 4, the wire feeding rate is decreased by AV, and the wire feedingforce of the first feed motor is increased by AF, and that of the secondfeed motor by AF the result being that AF AF, AF Thus, the first andsecond feed motors are again placed in an equilibrium state. Thedrooping degrees of M,, and M,, are so selected that the value of AV,will not have a substantial effect on the welding operation.

For adjusting the wire feeding rate, the operational characteristiclines of the first and second feed motors are set at M and Mrespectively by adjusting the resistance value of the resistor 30 inFIG. 3, whereby a wire feeding rate of V is obtained when the wirefeeding force F is F, F The relationship between the wire feeding forceand the wire feeding rate of either one of these two motors is notrestricted to that shown in FIG. 4 but the drooping degree of thecharacteristic line may optionally be set to some extent and a risingcharacteristic may even be employed. In case of the latter, however,stable control of the wire feeding becomes difficult. In this event, thedrooping degree of the characteristic line of the motor is madesubstantially the same as that of the other motor and by so doing it ispossible to control the wire feeding with the highest stability.

Although the invention has been described in terms of a particularembodiment wherein the wire is'fed at a substantially constant rate, itshould be understood that the apparatus of the invention may be designedso that the wire feeding rate can be increased or decreased according tothe value of the arc voltage, by arranging such that the arc voltage ora voltage in proportion to the arc voltage may be impressed in place ofthe secondary coil 26 of the transformer in the circuit of FIG. 3.

The embodiment shown in FIG. 3 is only illustrative, and the same effectmay also be obtained by employing, in lieu of the silicon controlledrectifier system, a system using a magnetic amplifier or an electrontube.

In the prior art apparatus, the feeding force imparted to the wire bythe second feed motor is substantially constant and is neither increasednor decreased commensurate with a change in the force required forfeeding the wire, the first feed motor only being responsive to such achange.

With such apparatus, the feeding force of the secondary feed motoroccasionally decreases to too low a value, so that it not only hasbecome impossible to increase the length of the second guide tube but insome instances it has been necessary to connect the first feed motordirectly with the contact tip of the torch or a contact tip fixture,without providing the second guide tube. Moreover, since the wirepushing force of the first feed motor only is increased, the wire tendsto be buckled at the entrance end of the first guide tube, necessitatinga greater feeding force.

In passing a wire through a guide tube of the same length and curvature,the wire can be passed through the guide tube much easier by pulling itthan by pushing it. It is known that where a pushing force, for example,of kg is required for passing a wire through a guide tube, a force ofonly about 15-20 kg is sufficient for passing the wire through the sameguide tube by pulling it.

1 In the prior art apparatus, the wire passing force is supplementedsolely by a pushing force when the force required for feeding the wirehas increased due to an increased difficulty in feeding the wire causedas by an increase in the bending degree of the guide tube. Therefore,not only has a great pushing force been required for achieving a stablefeeding of the wire, but also there has been the fear of the wire beingbuckled and hence satisfactory wire feeding has not always beenattained.

In the apparatus of the present invention, as contrasted thereto, thefeeding forces of both the first and second feed motors are increasedcommensurate with an increase in the force required for feeding the wire(wire feeding load). Therefore, the wire passing through the first guidetube is subject to not only an increasing pushing force but also anincreasing pulling force, which prevents the wire from buckling moreeffectively and facilitates feeding of the wire. According to thepresent invention, therefore, it is possible to increase the length ofthe first guide tube and hence the radius of movable range of thewelding torch can be increased and the maneuverability of the apparatuscan be improved.

In FIG. 4, a motor having a greater feeding force is used as the firstfeed motor but this need not always be the case. Namely, satisfactoryoperation can also be obtained by using a motor having thecharacteristic represented by M in FIG. 4 as the second feed motor and amotor the characteristic represented by M as the first feed motor.Further, satisfactory operation can be obtained by locating the motor21, shown in FIG. 3, in a position closer to the torch and the motor 22in a position closer to the wire reel.

The relative position and characteristic of these motors may be selectedso as to be suited to a particular apparatus embodying the presentinvention. For instance, where the second feed motor is to beaccommodated in the welding torch, it must be small in size, compact inform and light in weight. Therefore, a motor is used as the second feedmotor which is smaller in feeding force than the first feed motor andhas a characteristic as shown in FIG. 4 relative to that of the firstfeed motor. On the other hand, where the second feed motor is to belocated closer to the torch between the first and.

second guide tubes, it is not subject to such a limitation with respectto weight and size. Therefore, the wire feeding force of the second feedmotor can be made large and may even be larger than that of the firstfeed motor. This is rather advantageous in that smooth wire feeding canbe more easily obtained because the wire pulling force becomes larger.

As may be understood from the foregoing, the welding apparatus of thisinvention is of great advantage in that smooth wire feeding can beobtained even when the length of the guide tube is increased, and alsoin that it is adaptable to a wide range of applications.

Speaking more specifically, it has been revealed that ac cording to thepresent invention wherein both the first feed motor and the second feedmotor which are substantially the same in drooping degree of thecharacteristic lines thereof participate in the setting of a wirefeeding rate and their shares of feeding force are substantiallyincreased according to an in crease in the feeding load, the apparatusis serviceable for practical use, with a wire of 1.2 mm or 1.6 mm indiameter, even when the first guide tube is 30 m and the second guidetube is 3 m in length, In contrast thereto, when motors of the samespecification as those mentioned in the present invention were used inthe conventional apparatus as the first and second feed motorsrespectively, the apparatus was not serviceable for practical weldingoperations at a welding site due to failure in smooth feeding of thewire and excessive bending of the first guide tube when the length ofthe first guide tube exceeded m and that of the second guide tubeexceeded 3 m.

For any speed setting, the best effect is obtained when the motors usedhave substantially the same drooping degree (of the speed vs. loadcharacteristic). Where the drooping degrees are not the same, the loadsharing effect of the two motors with respect to an increasing feedingloadis great when the drooping degree of one motor is 3 or smallerrelative to l of the other motor, and an appreciable effect can beobtained when the drooping degree of one motor is up to 5 relative to lof the other motor. Where the drooping degrees of the motors are not thesame or varied from each other intentionally, feed-- ing of the wire canbe attained more efficiently when the motor of greater drooping degreeis used as the first feed motor and the motor of the smaller droopingdegree as the second feed motor. It will be obvious, however, that inpractice the relative characteristic and position of these motors shouldbe determined in consideration of the conditions corresponding to thesize, weight and manner of use of the motors.

As has been described above, in the semi-automatic or automatic weldingapparatus according to the present invention two or more motors, eachhaving a wire feeding force vs. wire feeding rate characteristic ofsmall drooping degree, i.e., a

characteristic approximating to the constant speed characteristic, areconnected with each other in parallel relation for feeding a consumablewelding electrode wire, so that the load shares taken by the individualmotors may be substantially increased as the wire feeding loadincreases. Therefore, efficient smooth wire feeding is ensured, evenwhen the wire guide tubes are long, and hence the apparatus of theinvention is adapted to a wide range of practical applications. Thus,the present invention is of great industrial advantage.

What is claimed is:

1. Apparatus for use in welding a work piece by an electric are producedbetween a consumable welding electrode and the work piece, saidapparatus comprising: a consumable welding electrode wire; a path alongwhich said electrode wire is fed towards said work piece; at least twomeans for feeding said electrode wire along said path, said feedingmeans being located at two remote positions along said path of saidelectrode wire; two motors for driving said two feeding means,respectively, said two motors having substantially the same drooping,approximate to a constant speed, characteristics; and means forcontrolling said two motors, said means comprising an AC power source, amotor circuit for connecting said two motors in parallel, a controlledrectifier connected between said power source and said motor circuit, acircuit for producing a desired reference voltage, and means forcontrolling the conduction of said controlled rectifier responsive tothe difference between said reference voltage and a voltage inducedacross said motor circuit.

2. A welding apparatus according to claim I, wherein said referencevoltage is variable in accordance with variation of a voltage developedacross said circuit.

1. Apparatus for use in welding a work piece by an electric arC producedbetween a consumable welding electrode and the work piece, saidapparatus comprising: a consumable welding electrode wire; a path alongwhich said electrode wire is fed towards said work piece; at least twomeans for feeding said electrode wire along said path, said feedingmeans being located at two remote positions along said path of saidelectrode wire; two motors for driving said two feeding means,respectively, said two motors having substantially the same drooping,approximate to a constant speed, characteristics; and means forcontrolling said two motors, said means comprising an AC power source, amotor circuit for connecting said two motors in parallel, a controlledrectifier connected between said power source and said motor circuit, acircuit for producing a desired reference voltage, and means forcontrolling the conduction of said controlled rectifier responsive tothe difference between said reference voltage and a voltage inducedacross said motor circuit.
 2. A welding apparatus according to claim 1,wherein said reference voltage is variable in accordance with variationof a voltage developed across said circuit.